When a cellular communication device is turned on (e.g., after a flight), the device has no or only little knowledge of what cellular networks might be available at the current site and on what frequencies. For this reason, the device initially performs a cell search procedure and scans frequencies where a cellular network might be found. During the frequency scan, multiple carrier frequencies in possibly multiple frequency bands are investigated as potential candidates for starting a network access procedure.
Due to the increased number of cellular telephones and other devices with cellular network access capabilities, the number of frequency bands for cellular communication is steadily increasing. Just recently, the bands for cellular services have been extended with Bands 40 (2300-2400 MHz, intended for TDD), Band 38 (2570-2620 MHz, intended for TDD), and Band 7 (2500-2570 and 2620-2690 MHz, intended for FDD). Consequently, more and more possible frequencies need to be scanned during the initial cell search procedure, and the cell search procedure generally takes more time.
Moreover, when Bands 7, 28 and 40 are scanned during a cell search procedure, the cellular communication device listens at frequencies that are close to the unlicensed ISM band (2400-2483.5 MHz). Should the device additionally support one or more further Radio Access Technologies (RATs) using this ISM band, the cell search procedure might be severely hampered. An example of an RAT operating in the ISM band is the BLUETOOTH communications standard. Another ISM band RAT that is gaining momentum in cellular communication devices is defined in the IEEE 802.11b/g standard.